This invention relates, generally, to external, hang-on filters for aquarium tanks and, more specifically, to a biological filter that attaches to the outflow of external, hang-on filters and provides abundant surface area for growth of aerobic bacteria and increased oxygen transfer into the aquarium water.
Tank mounted, or hang-on, external filters are used to mechanically and chemically filter and purify aquarium water to eliminate undesirable wastes and toxins and to maintain a healthy, aquarium environment. Such filters also typically include biological filters for removing fish waste byproducts such as ammonia, nitrates and nitrites from the water. These biological filters provide a surface for the growth of aerobic bacteria which help to break down the fish waste byproducts and prevent toxic waste buildup in the aquarium.
A known biological filter for an external, hang-on, aquarium comprises plastic plates having convoluted channels that is placed within the filter container. The problem with this filter is that the channels are under water and do not allow aerobic bacterial growth, only anaerobic. Also there is no additional oxygen exchange into the aquarium water. To remedy this problem a venturi type air suction valve and tube is place through the filter case, sending air to the bottom of the convoluted channel wall, providing air. (See, for example, U.S. Pat. No. 5,728,293). The problem with a venturi type air suction valve is that it is quite noisy due to the air suction and is, therefore, unacceptable to most hobbyists.
A second method of accomplishing the desired result of aerobic bacterial growth and oxygen exchange, has been to provide a wheel of convoluted reinforced paper, (similar to a paddle wheel) at the filter outflow. (See, for example, U.S. Pat. No. 5,423,978). This apparatus improves the growth of aerobic bacteria, but the wheel is a moving part and, after extended use, often jams due to the accumulation of fish tank crude. Also, the wheel will often make noise as it moves with the water.
An object of the present invention is to provide a biological filter that solves the problems of known biological filters and provides improved growth of aerobic bacteria and enhanced oxygen exchange with the aquarium water.
In accordance with the above and other objects, a biological filter for an aquarium hang-on filter according to the present invention comprises an external filter that attaches to the outflow of the aquarium hang-on filter. The biological filter includes a multiplicity of convoluted plastic channels for the flow and agitation of water. These channels provide abundant surface area for aerobic bacteria to form and, by placement at the outflow of the filter, there is sufficient air exchange to allow aerobic bacteria growth. Additionally, the attachment provides the beneficial function of increasing oxygen transfer into the water. The water leaving the filter is split and agitated allowing more surface contact of the water with the air. This increased oxygenation of the aquarium water is beneficial to the fish. These advantageous functions are accomplished without moving parts.